|Days||third gestational week|
|Gives rise to||somites|
In the developing vertebrate embryo, the somitomeres are loose masses of paraxial mesoderm derived cells that form along each side of the neural tube towards the end of the third gestational week. The approximately 50 pairs of somitomeres begin developing in the cranial (head) region, continuing in a caudal (tail) direction until the end of week four.
The remaining somitomeres, likely driven by periodic expression of the hairy gene, begin expressing adhesion proteins such as N-cadherin and fibronectin, compact, and bud off forming somites. The somites give rise to the vertebral column (sclerotome), associated muscles (myotome), and overlying dermis (dermatome).